Semiconductor processing methods, and methods of forming flash memory structures

ABSTRACT

Some embodiments include methods of reflecting ions off of vertical regions of photoresist mask sidewalls such that the ions impact foot regions along the bottom of the photoresist mask sidewalls and remove at least the majority of the foot regions. In some embodiments, trenches may be formed adjacent the photoresist mask sidewalls in a material that is beneath the photoresist mask. Another material may be formed to have projections extending into the trenches. Such projections may assist in anchoring said other material to the material that is beneath the photoresist mask. In some embodiments, the photoresist mask is utilized for patterning flash memory structures. Some embodiments include semiconductor constructions having materials anchored to underlying materials through fang-like projections.

TECHNICAL FIELD

Semiconductor constructions, semiconductor processing methods, andmethods of forming flash memory structures.

BACKGROUND

Photolithographic processing is commonly utilized for patterningmaterials during semiconductor processing. In photolithographicprocessing, photoresist is exposed to patterned radiation and thendeveloped to form a patterned photoresist mask. The pattern of thephotoresist mask may be subsequently transferred to underlying materialswith one or more suitable etches. Alternatively, or additionally, thephotoresist mask may be utilized to block a portion of the underlyingsubstrate during implant of dopant into the substrate.

It is often desired to form the patterned photoresist mask to havevertical sidewalls extending from the underlying substrate. A problemthat may occur during photolithographic processing is that the sidewallsmay only be vertical along the upper portions, and may have non-verticalexcess material at the interface of the photoresist mask and theunderlying substrate. Such excess material may be referred to as footregions at the base of the photoresist mask. The foot regions complicatesubsequent utilization of the mask, regardless of whether the mask isutilized to pattern an etch or is utilized for patterning a dopantimplant.

It is desired to develop methods for treating photoresist masks whichremove the foot regions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 show diagrammatic cross-sectional views of a fragment of asemiconductor construction, and illustrate process stages duringphotolithographic processing in accordance with an example embodiment.

FIG. 4 shows the fragment of FIGS. 1-3 at a process stage subsequent tothat of FIG. 3.

FIG. 5 shows the fragment of FIGS. 1-3 at a process stage subsequent tothat of FIG. 3 in accordance with another embodiment.

FIGS. 6-11 show the fragment of FIG. 5 at process stages subsequent tothat of FIG. 5.

FIG. 12 shows a top view of the fragment of FIG. 8.

FIG. 13 shows a top view of a prior art fragment at a process stageanalogous to that of FIG. 12.

FIG. 14 shows a diagrammatic, cross-sectional view of a fragment of asemiconductor construction in accordance with an embodiment.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

In some embodiments, a dry trim process is utilized to control and/orremove a foot region from a patterned photoresist mask. Such removal maybe accomplished utilizing concentration of ions proximate sidewalls ofthe photoresist mask. In some embodiments, the photoresist mask isformed over a first material, and trenches are formed in the firstmaterial adjacent sidewalls of the photoresist mask as the foot regionsare removed. Subsequently, a second material may be deposited adjacentthe sidewalls and with projections extending into the trenches. Suchprojections may assist in anchoring the second material to the firstmaterial.

Example Embodiments are Described With Reference to FIGS. 1-14.

Referring initially to FIG. 1, such shows a semiconductor construction10 at a process stage during fabrication of flash memory devices.Construction 10 comprises a base semiconductor material 12. The basesemiconductor material may comprise, consist essentially of, or consistof silicon; and may, for example, correspond to monocrystalline siliconlightly background doped with p-type dopant. Base semiconductor material12 may be considered a semiconductor substrate or a portion of asemiconductor substrate. To aid in interpretation of the claims thatfollow, the terms “semiconductive substrate,” “semiconductorconstruction” and “semiconductor substrate” mean any constructioncomprising semiconductive material, including, but not limited to, bulksemiconductive materials such as a semiconductive wafer (either alone orin assemblies comprising other materials), and semiconductive materiallayers (either alone or in assemblies comprising other materials). Theterm “substrate” refers to any supporting structure, including, but notlimited to, the semiconductive substrates described above. Although base12 is shown to be homogenous, the base may comprise numerous layers insome embodiments. For instance, base 12 may correspond to asemiconductor substrate containing one or more layers associated withintegrated circuit fabrication. In such embodiments, such layers maycorrespond to one or more of metal interconnect layers, barrier layers,diffusion layers, insulator layers, etc.

Tunnel dielectric 14 is formed over base 12. The tunnel dielectric maycomprise any suitable composition or combination of compositions; andmay, for example, comprise, consist essentially of, or consist ofsilicon dioxide.

A charge-retaining material 16 is formed over tunnel dielectric 14. Thecharge-retaining material may comprise a floating gate (for instance,polycrystalline silicon) or may comprise charge-trapping material (forinstance, silicon nitride). Although the charge-retaining material isshown to be homogeneous, in some embodiments it may comprise multipledifferent compositions, such as, for example, nanodots embedded withindielectric material.

A blocking dielectric 18 is over the charge-retaining material. Theblocking dielectric may comprise any suitable composition or combinationof compositions; and may, for example, comprise, consist essentially of,or consist of one or more of silicon nitride, silicon dioxide, or any ofvarious high-k materials (with high-k materials being materials having adielectric constant greater than that of silicon dioxide).

Control gate material 20 is formed over the blocking dielectric. Thecontrol gate material may comprise any suitable composition orcombination of compositions; and may, for example, comprise, consistessentially of, or consist of one or more of various metals,metal-containing compositions, and conductively-doped semiconductormaterials.

The tunnel dielectric 14, charge-retaining material 16, blockingdielectric 18 and control gate material 20 may be together considered agate stack 22, in that the layers may ultimately be patterned into flashmemory gates.

A patterning mask material 24 is formed over gate stack 22. Thepatterning mask material may be a carbon material, and may, for example,comprise, consist essentially of, or consist of amorphous carbon.

A hard masking material 26 is formed over material 24. The hard maskingmaterial may correspond to a deposited antireflective coating (DARC);and may thus comprise, consist essentially of, or consist of siliconoxynitride. DARC is an example material 26, and material 26 may compriseother compositions in other embodiments (the composition of material 26may be electrically insulative, electrically conductive, orsemiconductive, depending on the application).

Material 28 is deposited over hard masking material 26. Material 28 maycomprise, consist essentially of, or consist of photoresist in someembodiments, and may be referred to as photoresist in some of theembodiments described herein.

As discussed above, the term “semiconductor substrate” may describeconstructions which include semiconductor material in combination withvarious layers and structures. Accordingly, the base 12, gate stack 22,carbon material 24 and hard masking material 26 may be togetherconsidered to be a semiconductor substrate in some embodiments.

Referring to FIG. 2, photoresist 28 is photolithographically patternedto form a patterned masking structure 30 from the photoresist. Structure30 may be referred to as a patterned photoresist mask, or alternativelyas a patterned feature. The patterned photoresist mask comprises, in theshown cross-sectional view, a pair of opposing sidewalls 32 and 34, andan upper surface 35 extending between the sidewalls.

The sidewalls 32 and 34 extend upwardly from an uppermost surface ofhard masking material 26. The sidewalls comprise upper regions 36 whichare substantially vertical (i.e., orthogonal relative to a planar uppersurface of material 26), and comprise lower regions 38 which arenon-vertical. The lower regions may be referred to as foot regions. Thefoot regions are generally undesired, and result from difficulties andproblems during photolithographic processing and development. The footregions may be considered excess photoresist material remaining at theinterface of the patterned photoresist mask with the underlying layer26. Ideally, the sidewalls 32 and 34 would extend vertically along theentire distance from the interface with underlying material 26 to theupper surface 35, rather than having the foot regions 38. Someembodiments include methods which may be utilized to either entirelyremove the foot regions, or to control a shape of the foot regions.

Referring to FIG. 3, construction 10 is exposed to etching conditionswhich remove some of the photoresist mask 30. Such etching conditionsmay lower the height of the mask (in other words, reduce the distancebetween upper surface 35 and the upper surface of layer 26), and alsomay reduce the lateral thickness of the photoresist mask (in otherwords, reduce the distance between sidewalls 32 and 34). The etchingconditions are shown to comprise ions 40 directed downwardly at thephotoresist mask. The ions are primarily normally directed, but havesome amount of lateral velocity. Therefore, some of the ions graze thevertical regions 36 of the sidewalls, as illustrated by the grazing ions41 in FIG. 3. Such grazing ions may reflect from the vertical regions ofthe surfaces and thereby be directed toward the foot regions 38. Thismay cause the foot regions to be subjected to more etching than otherregions of the photoresist mask, which may cause more rapid removal ofthe foot regions than other regions of the photoresist mask. Areashaving some etching due to the reflections are diagrammaticallyillustrated as regions 39 in FIG. 3. The regions 39 having additionalion etching may be referred to as areas where some ion focusing occurs.

The rapid removal of material from regions 39 may ultimately result inremoval of at least the majority of the excess material of the footregions, which may modify the sidewalls 32 and 34 so that they nowextend vertically all the way to the upper surface of material 26 (asshown in FIG. 4).

The concentration (or focusing) of ions into regions adjacent thevertical sidewalls may be considered microtrenching (or alternatively,profile trenching). Two mechanisms that have been proposed to explainmicrotrenching are: (1) that specular ion scattering occurs fromsidewall surfaces at grazing incidence, and (2) that ion deflectionoccurs due to differential charging of microstructures. In the priorart, microtrenching is a problem which is to be avoided duringsemiconductor fabrication. Some embodiments of the present inventionutilize the prior art problem of microtrenching for benefit duringpatterning of masking features.

Some example conditions that may be utilized to induce ion focusingduring patterning of feature 30 are as follows. A bias may be from about100 volts to about 1000 volts (for instance, from about 150 volts toabout 400 volts), a treatment time may be from about five seconds toabout two minutes (for instance, from about 10 seconds to about 30seconds), a pressure within a treatment chamber may be less thanatmospheric (for example, may be about 10 millitorr), and the ions maybe formed from any gases that isotropically etch material of feature 30.For instance, if feature 30 consists of photoresist, the ions may beformed from oxygen and/or hydrofluorocarbons and/or halogen-containmaterials and/or N₂.

Referring to FIG. 4, construction 10 is shown after sufficient etchingto reduce a width of photoresist mask by about one-half, and tosubstantially entirely remove foot regions 38 (FIG. 2). The entirety ofsidewalls 32 and 34 extend vertically from the interface with material26 to the upper surface 35 of masking feature 30 at the processing stageof FIG. 4. Accordingly, the etching of FIG. 3 may be considered to haveextended the verticality of the upper regions 36 (FIG. 2) of thesidewalls to the lower regions 38 (FIG. 2) of the sidewalls.

The construction of FIG. 4 illustrates one embodiment for patterning amask. Another embodiment is shown in FIG. 5. The embodiment of FIG. 5shows trenches (or cavities) 40 formed into hard masking material 26 bythe ion reflections utilized to remove the foot regions 38 (FIG. 2). Thetrenches 40 are at the bases of sidewalls 32 and 34, and may beconsidered to be formed along the vertical sidewalls, or may beconsidered to be extensions of the vertical regions of the sidewallsinto the material 26. In the shown embodiment, the trenches extend onlypart of the way through material 26.

In subsequent processing, patterned mask 30 is utilized for imparting apattern to the gate stack 22. The processing for utilizing the patternedmask to impart such pattern may be the same regardless of whether theprocessing initiates from the construction of FIG. 4 (in other words,initiates from a construction lacking trenches adjacent the mask), orinitiates from the construction of FIG. 5 (in other words, initiatesfrom a construction having trenches adjacent the mask). However, thetrenches of FIG. 5 may provide some advantages, as discussed below.FIGS. 6-11 describe patterning of the gate stack relative to theembodiment initiating from the construction of FIG. 5. The inventionincludes an analogous embodiment in which similar patterning may beconducted initiating from the construction of FIG. 4.

Referring to FIG. 6, a sacrificial material 42 is formed over patternedmask 30 and within cavities 40. Sacrificial material 42 may comprise anysuitable composition or combination of compositions, and may, forexample, comprise, consist essentially of, or consist of silicon dioxideor silicon nitride.

Referring to FIG. 7, sacrificial material 42 is anisotropically etchedto form the material into a pair of masking structures 44 and 46 onopposing sides of mask 30. The masking structures 44 and 46 are alongthe opposing sidewalls 32 and 34 of the patterned mask, respectively.

Referring to FIG. 8, patterned mask 30 (FIG. 7) is removed to leave agap 48 between the masking structures 44 and 46. The masking structures44 and 46 have projections of material 42 extending into layer 26 (theportions of material 42 within cavities 40), and such projections mayassist in anchoring material 42 to material 26. This is an advantage ofutilizing the embodiment of FIG. 5 that had the cavities 40, relative toutilizing the embodiment of FIG. 4 that lacked such cavities.

The masking structures 44 and 46 are formed at higher density than theoriginal photoresist pattern, and in some embodiments the process ofreplacing the photoresist masking structure with the masking structures44 and 46 may be a method for halving the pitch between maskingstructures (or doubling the number of masking structures across a unitarea).

Referring to FIG. 9, the pattern of masking structures 44 and 46 istransferred into layer 26 with an etch of the material of layer 26.

Referring to FIG. 10, sacrificial material 42 (FIG. 9) is removed, andthe pattern of hard masking material 26 is transferred into carbonmaterial 24 with an etch.

Referring to FIG. 11, the pattern of carbon material 24 (FIG. 10) istransferred into gate stack 22 with one or more suitable etches, andmaterials 24 and 26 (FIG. 10) are removed. Such forms the gate stacksinto gates 50 and 52 which may then be incorporated into flash memorycells.

FIGS. 12 and 13 illustrate an advantage that may be obtained utilizingsome embodiments relative to the prior art. FIG. 12 shows a top view ofconstruction 10 at the processing stage of FIG. 8, and FIG. 13 shows atop view of a prior art construction at a similar processing stage. Thepatterned masks 44 and 46 are lines extending across material 26, and inthe embodiment of FIG. 12 such lines are straight and parallel with oneanother. In contrast, in the prior art construction of FIG. 13 similarlines 44 and 46 serpentine across surface 26 and do not remain parallelwith one another. The reason that the prior art lines of FIG. 13serpentine is due to the foot regions 38 (FIG. 2) having not beenremoved in prior art processing, so that the lines 44 and 46 wobble onsuch foot regions and shift on material 26 due to instability induced bysuch wobbling. The embodiment of FIG. 12 eliminated the wobbling byremoving the foot regions. In embodiments in which masking materials 44and 46 have projections anchored in cavities (for instance, theprojections anchored in cavities 40 of FIG. 8), such anchoring canfurther assist in alleviating shifting of the masking materials on asurface of material 26.

FIG. 14 shows an enlarged view of masking structure 44 and underlyingmaterial 26 at the processing stage of FIG. 8. The masking structure isshown to comprise a projection of material 42 within cavity 40. Suchprojection is generally indicated by the label 60. The projection has apointed bottom region 62 and a pair of sidewalls 63 and 65 extendingupwardly from such pointed bottom region. The sidewall 65 issubstantially vertical, while the sidewall 63 is angled away fromvertical and extends to a curved region 65. The projection 60 is shapedsomewhat like a fang, and accordingly may be referred to as a fang-likeprojection.

The size of the projection may be controlled by the conditions utilizedduring the patterning of FIG. 3. The masking structure 44 may beconsidered to comprise a total (or overall) height extending from thelowermost surface of the fang to the top surface of the maskingstructure, with such height being indicated by the label 70 in FIG. 14.The masking structure may also be considered to comprise a lateral widthextending from one of the sidewalls in the shown cross-sectional view tothe other of the sidewalls, with such lateral width being indicated bythe label 72 in FIG. 14. The fang-like projection has a height from thelowermost surface of the projection to the top surface of material 26,with such height being labeled 74 in FIG. 14. The fang-like projectionalso has a lateral width, with such with being labeled 76 in FIG. 14. Insome embodiments, the height of the fang-like projection may be fromabout five percent to about 50 percent of the total overall height ofthe masking structure 44; and the width of the projection may be fromabout five percent to about 100 percent of the total width of themasking structure.

Although the embodiments described above are for removing foot regionsproximate photoresist, in other embodiments analogous processing may beutilized to remove foot regions adjacent other materials. Also, althoughthe embodiments illustrate anchoring sacrificial materials onto othermaterials through the illustrated fang-like projections, in otherembodiments materials which are not sacrificial may be anchored throughanalogous fang-like projections.

Although example embodiments are describe above with reference toformation of flash memory, in other embodiments the methods describedherein may be utilized during fabrication of other structures. Themethods may be particularly useful during fabrication of constructionshaving regular line and space features, such as, for example, othermemory arrays (for instance, dynamic random access memory (DRAM)arrays).

In compliance with the statute, the subject matter disclosed herein hasbeen described in language more or less specific as to structural andmethodical features. It is to be understood, however, that the claimsare not limited to the specific features shown and described, since themeans herein disclosed comprise example embodiments. The claims are thusto be afforded full scope as literally worded, and to be appropriatelyinterpreted in accordance with the doctrine of equivalents.

1. A method of forming a flash memory structure, comprising: forming apatterned photoresist mask over a semiconductor substrate, thephotoresist mask comprising, in at least one cross-sectional view, apair of opposing sidewalls extending upwardly relative to the substrate,the sidewalls comprising upper vertical regions and lower non-verticalregions; the substrate comprising a semiconductor base and a gate stackover the semiconductor base; the gate stack including in ascending orderfrom the semiconductor base, tunnel dielectric, charge-retainingmaterial, blocking dielectric, and control gate material; the substratefurther comprising carbon material over the control gate material, andhard masking material over the carbon material; the photoresist maskbeing formed over the hard masking material; exposing the patternedphotoresist mask to microtrenching conditions to remove portions of thephotoresist mask from the non-vertical regions and thereby extend thevertical regions to the hard masking material, and to form cavities inthe hard masking material; forming a sacrificial material over thepatterned photoresist mask and along the opposing sidewalls, thesacrificial material extending into the cavities; anisotropicallyetching the sacrificial material to form masking structures along theopposing sidewalls of the photoresist mask; removing the photoresistmask; transferring a pattern of the masking structures into the hardmasking material, carbon material, and gate stack with one or moresuitable etches; and after transferring that pattern of the maskingstructures into the hard masking material, removing the maskingstructures.
 2. A semiconductor processing method, comprising: forming apatterned photoresist mask over a semiconductor substrate, thephotoresist mask comprising, in at least one cross-sectional view, apair of opposing sidewalls extending upwardly relative to the substrate,the sidewalls comprising upper vertical regions and lower non-verticalregions; exposing the patterned photoresist mask to microtrenchingconditions to remove portions of the photoresist mask from thenon-vertical regions and to also extend the vertical regions into thesubstrate to form cavities in the substrate adjacent the patternedphotoresist mask; forming a sacrificial material over the patternedphotoresist mask and along the opposing sidewalls, the sacrificialmaterial extending into the cavities; anisotropically etching thesacrificial material to form masking structures along the opposingsidewalls of the photoresist mask; removing the photoresist mask;transferring a pattern of the masking structures into the substrate withone or more suitable etches; and after transferring that pattern of themasking structures into the substrate, removing the masking structures.3. The method of claim 1 wherein the cavities do not extend entirelythrough the hard masking layer.
 4. The method of claim 1 wherein thehard masking material consists of silicon oxynitride, and wherein thesacrificial material consists of silicon dioxide or silicon nitride. 5.The method of claim 1 wherein an individual sacrificial material maskingstructure has a projection extending into a cavity, and has a totalheight from a lowermost region of projection to an uppermost surface ofthe masking structure; and wherein the projection comprises from about5% to about 50% of said total height.
 6. The method of claim 1 whereinan individual sacrificial material masking structure has a projectionextending into a cavity, and has a lateral width; and wherein theprojection comprises from about 5% to about 100% of said lateral width.7. The method of claim 1 wherein: an individual sacrificial materialmasking structure has a projection extending into a cavity; theindividual masking structure has a total height from a lowermost regionof the projection to an uppermost surface of the masking structure; theprojection comprises from about 5% to about 50% of said total height; anindividual masking structure has a lateral width; and the projectioncomprises from about 5% to about 100% of said lateral width.